The present invention relates to an engine control system for internal combustion engines, or more in particular, to an engine control system having the functions of fine adjustment of control values including idle engine speed and mixture ratio.
Conventional engine control systems have a mechanism for fine adjustment of such values as a control target. An example of adjustment of idle engine speed is disclosed, for example, in "Automotive Engineering" No. 7, 1986, p. 83 to p. 84.
In the aforementioned prior art system, the idle set engine speed is finely adjusted in such a manner that a constant voltage is applied across a variable resistor provided for an engine control system, and the neutral potential thereof is read by an A/D converter thereby to change the set engine speed in accordance with the potential.
In this conventional system, however, the fact that the set value is easy to change by operation of the variable resistor adversely affects the tamperproofness, and that, a movable part provided therein poses the problem of a deviation of the set value due to vibration or damage to the movable part by improper operation.